1. Field of the Invention
This invention generally relates to hermetic motor compressors which are usually used in a refregirator, an air conditioner and the like.
2. Description of the Prior Art
Conventional hermetic motor compressors are apt to be noise sources since resonance phenomena often occur between the compressor unit and the hermetic casing thereof.
Therefore, countermeasures, such as the adoption of a spherical shape for the hermetic casing have been taken hitherto. However, such a countermeasure merely makes the stiffness of the casing high to deviate the resonance frequency toward a higher frequency so that it has a very little effect on prevention of vibrations of lower modes and the resonance phenomena between respective excitation points. As a result, noise reduction to a sufficient extent could not be obtained with such a conventional countermeasure.
Namely, when measuring the lower mode vibrations in a conventional cylindrical or spherical casing such as shown in FIG. 1 or FIG. 2, it will be understood that vibrations having their antinode or loop at an excitation point X will occur at typical second (2000 Hz), third (2400 Hz) and fourth (3900 Hz) modes as shown in FIG. 3, FIG. 4 and FIG. 5. It is considered that this is caused by the fact that the horizontal cross-section of the hermetic casing is of a circular shape. Although the vibrations in the above described examples are caused by a single exiting point, if there are another exciting point, besides respective phases are opposite to each other, then it is predicted that a superimposition phenomenon with respect to both vibrations occurs to increase the degree of the vibrations.